Marrow culture studies will be performed using the soft agar assay for detection of granulocyte-macrophage stem cells (CFU-c). Detection of qualitative defects in CFU-c proliferation associated with acute myeloid leukemia and preleukemic states will be used diagnostically and prognostically to monitor patients at first diagnosis and during the course of chemotherapy. Serial studies will be carried out in patients with chronic myeloid leukemia in order to detect at an early age emerging acute phase clones in stable chronic phase disease. Changes in marrow culture characteristics in blastic CML together with terminal transferase assay will be used for identification of lymphoblastic transformation and of mixed myeloblastic-lymphoblastic transformation. The role of suppressor cells will be investigated in patients with aplastic and refractory anemias, preleukemia and idiopathic neutropenias. A murine system to continuous marrow culture will be adapted to human studies and used as an assay for pluripotential stem cells or as a means of clonal segregation of coexisting normal and leukemic stem cells in remission bone marrow. Using this system, cell lines will be established from AML and CML patients and subjected to functional characterization. The expression of Ia antigen on normal and leukemic stem cells will be compared.